12,576 research outputs found
G181.1+9.5, a new high-latitude low-surface brightness supernova remnant
More than 90% of the known Milky Way supernova remnants are within 5 degrees
of the Galactic Plane. We present the discovery of the supernova remnant
G181.1+9.5, a new high-latitude SNR, serendipitously discovered in an ongoing
survey of the Galactic Anti-centre High-Velocity Cloud complex, observed with
the DRAO Synthesis Telescope in the 21~cm radio continuum and HI spectral line.
We use radio continuum observations (including the linearly polarized
component) at 1420~MHz (observed with the DRAO ST) and 4850~MHz (observed with
the Effelsberg 100-m radio telescope) to map G181.1+9.5 and determine its
nature as a SNR. High-resolution 21~cm HI line observations and HI emission and
absorption spectra reveal the physical characteristics of its local
interstellar environment. Finally, we estimate the basic physical parameters of
G181.1+9.5 using models for highly-evolved SNRs. G181.1+9.5 has a circular
shell-like morphology with a radius of about 16~pc at a distance of 1.5 kpc
some 250 pc above the mid-plane. The radio observations reveal highly linearly
polarized emission with a non-thermal spectrum. Archival ROSAT X-ray data
reveal high-energy emission from the interior of G181.1+9.5 indicative of the
presence of shock-heated ejecta. The SNR is in the advanced radiative phase of
SNR evolution, expanding into the HVC inter-cloud medium with a density of
1^{-3}$. Basic physical attributes of G181.1+9.5 calculated with radiative
SNR models show an upper-limit age of 16,000 years, a swept-up mass of more
than 300 solar masses, and an ambient density in agreement with that estimated
from HI observations. G181.1+9.5 shows all characteristics of a typical mature
shell-type SNR, but its observed faintness is unusual and requires further
study.Comment: A&A accepted, 11 pages, 13 figure
The band electrode: Ongoing experience with a novel turp loop to improve hemostasis in 265 patients
Introduction: Intraoperative bleeding, one of the major complications of conventional transurethral resection of the prostate ( TURP), has led to a search for various alternative methods of tissue ablation in patients with benign prostatic hyperplasia. In 1996, we introduced the newly designed Band Electrode, which combines a high degree of resection efficiency with a better hemostasis. Material and Methods: 265 consecutive patients with prostatism underwent TURP with the Band Electrode. This modified loop electrode does not consist of a thin wire but is rather a flat metal band with a width of 1.2 mm. International prostate symptom score (IPSS), Life Quality Index ( L), peak urine flow and postvoid residual urine were evaluated pre- and postoperatively. Additionally, electrical parameters have been recorded with a specially designed high-frequency generator. Results: Median IPSS decreased from 23 preoperatively to 8 and 9 at 12 (n = 194) and 24 months ( n = 172), respectively (p < 0.001). Life Quality Index ( L) dropped from 4 to 2 and 2, respectively (p < 0.001). Peak urine flow increased from 8.2 ml/s to 18.2 (at postoperative day 3), 17.8 and 17.4 ml/s, respectively (p < 0.001). Median postvoid residual urine decreased from 77 to 15, 22 and 21 ml, respectively (p < 0.001). Resected tissue mass averaged 25 (8 - 102) g, resection time was 36.5 ( 18 - 82) min. Indwelling catheters were removed 32 ( 24 - 72) h postoperatively. None of the patients required blood transfusions or showed signs of a TUR syndrome. Despite a 1.3 times higher power need, the total energy application in vivo was comparable to conventional TURP. Conclusions: This simple exchange of active electrodes leads to a superior hemostasis and thus safety in TURP. Resection speed, tissue ablation and total energy need remain identical. Copyright (C) 2004 S. Karger AG, Basel
Synchrotron Polarization at High Galactic Latitude
We present preliminary results from mapping the high-latitude Galactic
polarization with the Effelsberg Telescope at 21 cm. Structures on the
resulting maps are mostly on the scale of several degrees. The results show
detection of polarization over most of the field, at the level of tens of
percent of the synchrotron emission. The evidence of more structure in Stokes Q
and U rather than in suggests the existence of Faraday
rotation.Comment: To be published in the proceedings of "The Cosmic Microwave
Background and its Polarization", New Astronomy Reviews, (eds. S. Hanany and
K.A. Olive
Magnetic fields of the W4 superbubble
Superbubbles and supershells are the channels for transferring mass and
energy from the Galactic disk to the halo. Magnetic fields are believed to play
a vital role in their evolution. We study the radio continuum and polarized
emission properties of the W4 superbubble to determine its magnetic field
strength. New sensitive radio continuum observations were made at 6 cm, 11 cm,
and 21 cm. The total intensity measurements were used to derive the radio
spectrum of the W4 superbubble. The linear polarization data were analysed to
determine the magnetic field properties within the bubble shells. The
observations show a multi-shell structure of the W4 superbubble. A flat radio
continuum spectrum that stems from optically thin thermal emission is derived
from 1.4 GHz to 4.8 GHz. By fitting a passive Faraday screen model and
considering the filling factor fne , we obtain the thermal electron density ne
= 1.0/\sqrt{fne} (\pm5%) cm^-3 and the strength of the line-of-sight component
of the magnetic field B// = -5.0/\sqrt{fne} (\pm10%) {\mu}G (i.e. pointing away
from us) within the western shell of the W4 superbubble. When the known tilted
geometry of the W4 superbubble is considered, the total magnetic field Btot in
its western shell is greater than 12 {\mu}G. The electron density and the
magnetic field are lower and weaker in the high-latitude parts of the
superbubble. The rotation measure is found to be positive in the eastern shell
but negative in the western shell of the W4 superbubble, which is consistent
with the case that the magnetic field in the Perseus arm is lifted up from the
plane towards high latitudes. The magnetic field strength and the electron
density we derived for the W4 superbubble are important parameters for
evolution models of superbubbles breaking out of the Galactic plane.Comment: 13 pages, 8 figures, accepted for publication in Astronomy &
Astrophysic
A Sino-German 6cm polarisation survey of the Galactic plane IX. HII regions
Large-scale radio continuum surveys provide data to get insights into the
physical properties of radio sources. HII regions are prominent radio sources
produced by thermal emission of ionised gas around young massive stars. We
identify and analyse HII regions in the Sino-German 6cm polarisation survey of
the Galactic plane. Objects with flat radio continuum spectra together with
infrared and/or Halpha emission were identified as HII regions. For HII regions
with small apparent sizes, we cross-matched the 6cm small-diameter source
catalogue with the radio HII region catalogue compiled by Paladini and the
infrared HII region catalogue based on the WISE data. Extended HII regions were
identified by eye by overlaying the Paladini and the WISE HII regions onto the
6cm survey images for coincidences. The TT-plot method was employed for
spectral index verification. A total of 401 HII regions were identified and
their flux densities were determined with the Sino-German 6cm survey data. In
the surveyed area, 76 pairs of sources are found to be duplicated in the
Paladini HII region catalogue, mainly due to the non-distinction of previous
observations with different angular resolutions, and 78 objects in their
catalogue are misclassified as HII regions, being actually planetary nebulae,
supernova remnants or extragalactic sources that have steep spectra. More than
30 HII regions and HII region candidates from our 6cm survey data, especially
extended ones, do not have counterparts in the WISE HII region catalogue, of
which 9 are identified for the first time. Based on the newly derived radio
continuum spectra and the evidence of infrared emission, the previously
identified SNRs G11.1-1.0, G20.4+0.1 and G16.4-0.5 are believed to be HII
regions.Comment: version after some minor corrections and language editing, full Table
2 - 5 will appear in CDS, accepted for publication in A&
A radio continuum survey of the southern sky at 1420 MHz. Observations and data reduction
We describe the equipment, observational method and reduction procedure of an
absolutely calibrated radio continuum survey of the South Celestial Hemisphere
at a frequency of 1420 MHz. These observations cover the area 0h < R.A. < 24h
for declinations less than -10 degree. The sensitivity is about 50 mK T_B (full
beam brightness) and the angular resolution (HPBW) is 35.4', which matches the
existing northern sky survey at the same frequency.Comment: 9 pages with 9 figures, A&A, in pres
Monotonically convergent optimization in quantum control using Krotov's method
The non-linear optimization method developed by Konnov and Krotov [Automation
and Remote Control 60, 1427 (1999)] has been used previously to extend the
capabilities of optimal control theory from the linear to the non-linear
Schr\"odinger equation [Sklarz and Tannor, Phys. Rev. A 66, 053619 (2002)].
Here we show that based on the Konnov-Krotov method, monotonically convergent
algorithms are obtained for a large class of quantum control problems. It
includes, in addition to non-linear equations of motion, control problems that
are characterized by non-unitary time evolution, non-linear dependencies of the
Hamiltonian on the control, time-dependent targets and optimization functionals
that depend to higher than second order on the time-evolving states. We
furthermore show that the non-linear (second order) contribution can be
estimated either analytically or numerically, yielding readily applicable
optimization algorithms. We demonstrate monotonic convergence for an
optimization functional that is an eighth-degree polynomial in the states. For
the 'standard' quantum control problem of a convex final-time functional,
linear equations of motion and linear dependency of the Hamiltonian on the
field, the second-order contribution is not required for monotonic convergence
but can be used to speed up convergence. We demonstrate this by comparing the
performance of first and second order algorithms for two examples
A Sino-German 6cm polarisation survey of the Galactic plane - VIII. Small-diameter sources
Information of small-diameter sources is extracted from the Sino-German 6cm
polarisation survey of the Galactic plane carried out with the Urumqi 25-m
telescope. We performed two-dimensional elliptical Gaussian fits to the 6cm
maps to obtain a list of sources with total-intensity and polarised flux
densities. The source list contains 3832 sources with a fitted diameter smaller
than 16 arcmin and a peak flux density exceeding 30 mJy, so about 5 times the
rms noise, of the total-intensity data. The cumulative source count indicates
completeness for flux densities exceeding about 60 mJy. We identify 125
linearly polarised sources at 6cm with a peak polarisation flux density greater
than 10 mJy, so about 3 times the rms noise, of the polarised-intensity data.
Despite lacking compact steep spectrum sources, the 6cm catalogue lists about
20 percent more sources than the Effelsberg 21cm source catalogue at the same
angular resolution and for the same area. Most of the faint 6cm sources must
have a flat spectrum and are either HII regions or extragalactic. When compared
with the Green Bank 6cm (GB6) catalogue, we obtain higher flux densities for a
number of extended sources with complex structures. Polarised 6cm sources
density are uniformly distributed in Galactic latitude. Their number density
decreases towards the inner Galaxy. More than 80 percent of the polarised
sources are most likely extragalactic. With a few exceptions, the sources have
a higher percentage polarisation at 6cm than at 21cm. Depolarisation seems to
occur mostly within the sources with a minor contribution from the Galactic
foreground emission.Comment: A&A accepted, 9 pages, 5 figures, Tables 1 and 2 are accessible from
http://zmtt.bao.ac.cn/6cm
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